Treatment of cellulosic sheet materials



June 6, 1944. v BAUER ETAL 2,350,336

TREATMENT OF CELLULOSIC SHEET MATERIALS Filed April 29. 1938 INVENTOR5.

I 2 72 M fi awltg, WTTORNEY.

Patented June 6, 1944 TREATMENT OF CELLULOSIC SHEET MATERIALS JordanBauer, Chicago, and Don M. Hurley, Geneva, 11]., assignors to Stein,Hall Manufacturing Company, Chicago, 111., a corporation of DelawareApplication April 29, 1938, Serial No. 204,978

3 Claims.

This invention relates to an improved method of treating cellulosicmaterials and to a new and improved product obtained thereby. Theinvention particularly relates to a new and improved method of preparingthe paper corrugating medium used to form the corrugated paper core ofcorrugated paper box board.

The expression "corrugating medium is used herein to describe the papersheet employed in making the paper core of corrugated paper board. Inordinary practice this material is an unsized paper usually made fromstraw, chestnut chip or kraft stock. The requirements of the corrugatedboard industry at the present time are that the paper used for thispurpose be of such a nature that it will corrugate properly and give arigid uniform corrugation.

Attempts to size the corrugating medium in order to obtain additionalrigidity in the corrugation have been unsuccessful largely due to theface that papers sized by prior methods were.

rendered incapable of being corrugated properly at high speeds.

Since the most satisfactory corrugating mediums from the standpoint ofoperation on the corrugating machine are relatively soft, unsizedpapers, the resultant corrugated paper board is also relatively soft anddoes not possess the strength and stiffness that might be desired.

Furthermore, due to the hydroscopic character of these types of papers,the corrugated paper board as made today tends to lose much of itsoriginal stiffness when subjected to high humidity conditions.

One of the objects of the present invention is V to provide a new andimproved method of treating corrugating media whereby they will give amore rigid corrugation which will substantially retain its stifl'nessunder high humidity conditions and yet, which can be readily corrugatedat high operating speeds. Another object of this invention is to providea means of producing a superior type of corrugating medium utilizing asa base the cheaper grades of waste paper stock which are at presentunsuitable for this purpose. Other objects will appear hereinafter.

It is characteristic of our invention that when unsized corrugated paperis treated by our method it is rendered stiffer and retains asubstantial degree of its stiffness even when saturated with water. Itfurthermore has a higher wet tear strength and resistance to sc'uflingor puncture than the original untreated paper. Although the wet strengthcharacteristics of the paper are increased by our method of treatment,the treated to paper substantially retains the water permeability andrapidity of water absorption that distinguished the original untreated,unsized paper. In fact, the water absorption rate is often greater.

It is characteristic of our invention that when a rosin or otherwisesized corrugated paper is treated by our method the wet strengthcharacteristics and scuff-resistance of the paper are improved without adetrimental effect in regard to such water-resistant characteristics aswere present in the original sized but untreated paper.

In either case, the mullen test of the dry treated paper may or may notbe higher than the original untreated paper depending upon the extent towhich it was treated.

Our process is adaptable to treating the corrugated paper as it is beingfabricated on the paper machine but also can be used to treat individualrolls of paper in the plant of the paper consumer. Our process,therefore, not only enables the paper manufacturer to treat his paper asit is being fabricated to obtain such desirable characteristics in thefinished paper sheet as is outlined herein, but also enables the paperconsumer to treat individual rolls of paper stock in his own corrugatingplant in such cases wherein it is desired to obtain a paper sheet withsuch characteristics.

Generally speaking, our process consists of apper sheet is thenimmediately wound up into a tight roll before the applied materials havea chance to dry and the treated rolls of paper allowed to stand aroundfor several days. During this period the liquid materials which wereapplied to the surface of the sheet gradually permeate into the paperand distribute themselves uniformly throughout the sheet. At the sametime the water-soluble urea-formaldehyde condensation product reacts inthe presence of the acid with the paper fibers, stiffening them andrendering them less capable of being softened or hydrated by water. As aresult the sheet develops a high wet strengthwhich is not merely asurface eifect but which is distributed uniformly throughout the sheet,both sides of the sheet showing the same degree of scuff-resistance.

By means of this method we overcome many of the disadvantages and highcost of treating paper with urea and formaldehyde compositions that werecharacteristic of prior art processes, and furthermore, we obtain apaper product which is quite different from that obtained by prior artprocesses and which is much more suitable for the purposes outlinedherein.

Because of the unique procedure followed in our process we are able toobtain a very definite effect on the paper even when we use relativelysmall amounts of urea, formaldehyde and acid. Thus, by merely dampeningthe surface of the paper sheet with the urea-formaldehyde compositionand acid solution, respectively, and immediately winding it into a tightroll and allowing it to stand for a period of time, we are able toobtain a uniform action on the paper fibers throughout the sheet withoutgreatly increasing its moisture content and necessitating a dryingoperation. This feature makes th cost of treatment very low and enablesthe use of the paper product in fields where low cost is one of theprimary factors. 7

According to our preferred method of practice, we dampen one side of thepaper sheet with a solution of a water-soluble condensation product offormaldehyde and urea. The water-soluble condensation product isprepared by heating at about 200 F. a mixture of 100 parts of 38%formaldehyde with 25 parts of urea. The resultant soluble condensationproduct may or may not be diluted with water before application to thepaper surface, depending upon the degree of effect desired.Subsequently, we dampen the epposite side of the paper sheet with awater solution comprising lactic acid and urea. The amount andproportion of urea and acid so applied are preferably so regulated thatthe amount of urea thus introduced onto the sheet will augment theamount of urea previously applied to the sheet in the form of acondensation product with formaldehyde to the extent that the finalamount of urea in the sheet will be such that foreach two moles offormaldehyde in the sheet at least one mole or slightly in excess of onemole of urea will be present. We then wind the treated paper into atight roll and allow it to stand until the applied materials permeatethroughout the paper structure and the reaction with the paper fibers issubstantially complete. The amount of lactic acid applied is preferablythe minimum amount that will accomplish the desired result, namely, theacceleration of the reaction between paper fibers and theformaldehyde-urea condensation product. The exact amount of acid usedwill depend upon the nature of the paper material being treated and thechar- 'acteristics desired in the treated sheet.

If desired, the procedure of applying the formaldehyde-urea condensationproduct to the sheet and then applying the urea lactic acid solution tothe sheet may be reversed without detriment to the final result.Furthermore, if a sheet with a somewhat one-sided effect is desired,both mixtures may be applied to the same side of the sheet instead of onopposite sides.

Although fair results may be obtained by using a mixture of urea,formaldehyde and lactic acid along with more or less water and applyingit immediately to the paper sheet in one operation, we have found that aprecipitate develops in such solutions on standing and a certain amountof their original effectiveness is lost. For this reason we prefer toapply the urea-formaldehyde solution and the acid solution to the paperin separate operations. Furthermore, we prefer to use aurea-formaldehyde solution or water-soluble condensation productthereof, wherein the proportion of formaldehyde is sumciently in excessof two moles of formaldehyde to one mole of urea that a clear, stable,water-soluble condensation product is obtained. Other stablewater-soluble, urea-formaldehyde condensation products prepared by othermeans are also suitable for our purpose.

Inasmuch as an excess of uncombined formaldehyde in the treated papersheet would impart g a disagreeable odor, we prefer to use a sufllcientamount of urea in the acid solution so that when both solutions havebeen applied to the paper a sufiicient or more than sumcient amount ofurea is present to completely combine all of the formaldehyde presentand render the finished sheet practically odorless. In such cases, ofcourse, where odor in the finished sheet is not a detrimental factor,this step in the procedure is not essential.

For the most part we prefer to use lactic acid or similar organic acidsas the catalyst to effect the reaction of the formaldehyde-ureacondensation product with the paper fibers. Mineral acids and salts ofan acid nature may also be used for this purpose but are not sodesirable due to their detrimental effect on the strength of the paperfiber. We have found that if the paper fibers throughout the sheet areto be uniformly acted upon by the urea-formaldehyde condensation productit is essential that the acid catalyst chosen be one that has theproperty of readily penetrating into and distributing itself throughoutthe paper structure. Lactic, citric, tartaric, phosphoric and benzenesulfonic acids are examples of acids having this property to asatisfactory degree.

Although for most purposes it is desirable to produce a paper sheetwherein the paper fibers have been acted on throughout, it is possiblethat for some purposes a paper sheet is desired wherein only the paperfibers adjacent the surface of the sheet are to be acted upon. This canbe readily accomplished by our method of treatment by using an alumsolution instead of lactic acid as the catalytic agent and applying bothacid and urea-formaldehyde solutions to the same side of the sheet. Analum solution is used as the catalytic agent in this instance because itdoes not have the property of readily penetrating into the paperstructure and as a result only the paper fibers adjacent the surface ofthe paper are acted upon.

We have found that in those cases wherein the more highly rosin sizedtypes of paper are to be treated with our process it is necessary inorder to secure astisfactory penetration of the treating solutions intothe sheet, to incorporate with each of the solutions a small amount ofacetic acid or other acid adapted to cut the sizing material.

The invention willbe further illustrated by the following description inconjunction with the accompanying drawing in which:

Figure 1 represents an apparatus suitable for treating a cellulosicsheet material in accordance with our invention where the cellulosicsheet has already been formed and wound up in a roll; and

Figure 2 illustrates another form of apparatus for incorporatingmaterials into a cellulosic paper sheet in accordance with ourinvention, said incorporation being effected while thepaper sheet isstill on the paper machine.

As shown in Figure l, a paper sheet or other tion these liquids mayconsist of a solution of a water-soluble urea-formaldehyde condensationproduct in one vessel and an acid solution or a mixture of acid and ureasolution in the other. Doctor rolls 30 and 32 are provided to regulatethe thickness of the film of liquid. As rolls 6 and I2 rotate in thedirection of the arrows, any excess liquid is removed therefrom by saiddoctor rolls 8!! and 32, thus providing for a uniform coating of thematerial to be applied.

The method of operation of the apparatus described in Figure 1 is asfollows. The sheet of paper A is unwound from a roll 2, passed beneathguide roll 4 and over coating roll 6 where the underside of the paper iscoated with either an acid solution, a mixture of urea-formaldehyde or awater-soluble condensation product of urea and formaldehyde. The coatingoperation is effected by direct contact between the roll 6 and papersheet A at the upper surface of roll 6. The

rial and carries a film thereof on its surface.

The uniformity of this film is controlled by doctor roll 30. Roll 6 maybe run at a rate equal to, faster, or slower than the rate of speed ofthe paper sheet A as it passes over the upper surface of said roll,depending upon the amount of material which it is desired to apply tothe paper. Likewise, the distance between roll 6 and doctor roll 30 maybe regulated as desired. After the paper sheet leaves roll 6 it passesover another guide roll 8 and thence around a third guide roll it tocoating roll [2, where the previously uncoated top surface of the paperis coated with a material different from that applied from coating roll6. Coating roll l2 rotates in a bath 28 of the material to be appliedwhich is contained in vessel 24. The uniformity of the film carried onthe surface of roll I2 is regulated by doctor roll 32. The speed of rolll2 may likewise be equal to, faster, or slower than the speed of papersheet A, depending largely upon the amount of material which it isdesired to apply. Regardless of whether the speeds of rolls 6 and I2 arethe same ordifierent it is preferable that their speeds be coordinatedby a coordinating means of any type such as is well known to thoseskilled in the art and the same relative speeds of the two rolls bemaintained.

As paper sheet A leaves coating roll I2 it is passed over a series ofguide rolls [4, l6 and I8 and then rewound on roll 20. It is to beobserved that when the roll is rewound the oppositely treated sides arebrought into contact with each other, that is, the top side of the paperis brought into contact with the bottom side and vice versa, thusbringing together the acid reacting material and the urea-formaldehydecondensation prodill] uct into relatively close relationship and therebygreatly facilitating a reaction adapted to increase the water-resistanceof the paper. The speed oi reaction may be increased somewhat by thetightness with which the roll 20 is wound. After the rewound roll hasbeen allowed to stand for several days or for even a lesser period thepaper is ready for use. Examination of the paper at this stage showsthat its stiffness has been increased. Likewise its wet strength hasbeen increased and it has greater resistance to soul! and puncture.

A corrugating medium treated in the manner above described may bedirectly corrugated from the paper roll with excellent results. Animproved corrugated paper board assembly is thus obtained having a morerigid corrugated core which will not deteriorate under high humidityconditions.

Thus it will be seen that the present invention provides a new andimproved method of making corrugated paper board assemblies wherein thepaper corrugating medium is treated from opposite sides with an acidsolution and a water soluble urea-formaldehyde reaction product, thanwound into a roll, allowed to stand until the reaction is substantiallycomplete within the fibers of the corrugating medium and is thereaftercorrugated directly from said roll in any conventional manner. Themethod of corrugating the corrugating medium and of forming it into acorrugated paper board assembly by attaching a liner or liners theretois known in the art per se and is shown, for example, in patents ofJordan V. Bauer, one of the joint inventors herein, U. S. 2,051,025 andU. S. 2,102,937.

Instead of carrying out our process as described with reference toFigure 1 in which we treat the paper when it is already in rolled formand after it has left the paper machine, we may also utilize our methodto advantage in the direct treatment of paper before it has left thepaper machine. This is accomplished by applying the acid solution andurea-formaldehyde condensation products to opposite sides of the papersheet at some point in the paper making process, preferably at a stagewhere the paper sheet is completely formed and has most of the waterremoved therefrom. Thus, as shown in Figure 2, we may apply an acidsolution and a urea-formaldehyde condensation product to opposite sidesof the paper sheet just before it passes between the calender rolls onthe paper machine. At this point the moisture content of the paper isbetween about 5% and 10% and the sheet is completely formed. Theadvantage of this method is the saving of a rewinding operation which isnecessary in the method described in Figure 1.

As illustrated in Figure 2, the paper sheet B, which is coming from thedrying rolls of the paper machine, passes between two guide rolls orpressing rolls 50 and 52 and thence through a series of calender rolls54 where it changes direction several times, finally being wound onto aroll 56. Just prior to the time that the sheet passes through rolls 50and 52 the acid solution or solution of acidic material and theurea-formaldehyde solutions are separately added to opposite sides ofthe paper sheet in any suitable manner, for example, by spraying, asillustrated, by means of nozzles 58 and 60 or by means of kiss rollssuch as illustrated in Figure 1. If desired the spraying operation maybe carried out between rolls'5ll, 52 and calender rolls 54, or the acidsolution and urea-formaldehyde solution may be added to the. paper sheetat the nip of roll 56 upon which the paper is being wound, that is tosay, at point 62. If this general method of adding the two solutions atthe nip 01' a roll is employed, both liquids may be added irom the sameside since the opposite side automatically becomes coated with liquid asthe paper is wound on the roll. This is another general method ofapplying our compositions to a cellulosic sheet and may be used inconjunction with a rewinding operation, as described in Figure 1,thereby avoiding the necessity of employing coating rolls.

The remainder of the apparatus shown in Figure 2 is conventional inpaper making machines and consists of a rewinding means, including aroll of paper 64, guide rolls 66 and 88, rewinding roll 10 and means '12for supporting rewinding roll 10. As soon as one roll is formed, anotherroll can be brought into place from the apex oi. the triangle 14.

In treating paper as previously described we prefer that the amount andconcentration of the treating solutions added to the paper be such thatnot more than abut6% to additional water will be added, thus making itunnecessary to dry thesheet after treatment for most purposes of usage.

Where urea is employed it may be replaced wholly or in part by itsanalogs or homologs in eluding substantially water-soluble ureas andthio-urea. It will be understood, however, that urea itself ispreferred. The formaldehyde used may be an ordinary grade offormaldehyde such as is sold in aqueous solution of about to 40%concentration having a specific gravity of .75 to .81. Other aldehydessimilar in reaction may also be employed, as, for example, acetaldol andparaformaldehyde. In general, compounds of this class may be referred toas formaldehyde forming compounds.

Methods of preparing stable condensation products of urea andformaldehyde which are miscible with water are well known in the art.These initial condensation products may be prepared under neutralconditions or in conjunction with various catalysts or agents designedto insure the stability of the condensation product. As previouslyindicated, we may also merely employ a mixture of urea and formaldehydewithout bringing about any initial condensation therein.

It will be understood that the treating solutions and the method oftreating cellulosic paper materials as above described may be variedconsiderably without departing from the essence of our invention. Itwill also be recognized that auxiliary materials may be used inconjunction with our method of treatment for various purposes, as, forexample, plasticizers such as glycerine, ethylene glycol, laurylsulphate, sodium lactate and/or mixtures of higher alcohol sulplates orsulphonated oils which have a wettlnl or dispersing action.

Having thus described the invention, what we claim as new and desire tosecure by Letters Patent of the United States is:

1. In the art of making corrugated paper board assemblies, the stepswhich comprise treating 0pposlte sides of a paper corrugating mediumwith an acid solution and a water-soluble urea-formaldehyde reactionproduct, the amount of said acid solution and said water-solubleurea-formaldehyde reaction product being sufllcient to increase thewater resistance of said paper corrugating medium without substantiallydecreasing its water permeability winding said corrugating medium in theform of a roll while it is still damp, allowing it to stand untilreaction is substantially complete within the fibers of the corrugatingmedium and thereafter corrugating said medium directly from said roll.

2. In the art of making corrugated paper board assemblies, the stepswhich comprise, treating a paper corrugating medium with urea,formaldehyde and an acid material in the presence of water inconcentrations such that the ratio of formaldehyde to urea isapproximately 2 moles of formaldehyde to 1 mole of urea and the amountof water is not greater than about 10% by weight of the papercorrugating medium, the proportions of said materials being sufllcientto merely dampen the paper corrugating medium and efiective to increasethe wet strength and the scuff-resistance without substantiallydecreasing the water absorptive capacity of the paper corrugatingmedium, allowing reaction to take place within the fibers of saidcorrugating medium, and thereafter corrugating said mediumand'incorporating it into a corrugated paper board assembly.

3. In the art of making corrugated paper board assemblies, the stepswhich comprise, treating a paper corrugating medium with urea,formaldehyde and an acid material selected from the group consisting oflactic acid, citric acid, tartaricacid, phosphoric acid and benzenesulfonic acids in the presence of water, the concentrations of said'materials corresponding to approximately 2 moles of formaldehyde to 1mole of urea with an amount of water not greater than about 10% basedupon the weight of the corrugating medium, said materials being added tothe corrugating medium in amounts merely sufllcient to dampen saidcorrugating medium and effective to increase the wet strength and thesour!- resistance without substantially decreasing the water absorptivecapacity of the corrugating medium.

JORDAN V. BAUER.

DON M. HAWLEY.

